Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior |
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Authors: | Yasuhiko Suzuki Hidetsugu Tanaka Toshiyuki Oshiki Kazuhiko Takai Terunori Fujita |
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Abstract: | New Ti and Zr complexes that bear imine–phenoxy chelate ligands, {2,4‐di‐tBu‐6‐(RCH=N)‐C6H4O}2MCl2] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C6F5; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C6F5), were synthesized and investigated as precatalysts for ethylene polymerization. 1H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or Ph3C]+B(C6F5)4]?/AliBu3 displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)?1 h?1, which is comparable to that for Cp2TiCl2] and Cp2ZrCl2], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C6F5 group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with Ph3C]+B(C6F5)4]?/AliBu3 activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)?1 h?1). 1H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /Ph3C]+B(C6F5)4]?/AliBu3 and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene. |
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Keywords: | catalysts complexes polymerization titanium zirconium |
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